Drosophila toll proteins control dorsal-ventral patterning and are thought to represent an ancient host defense mechanism. In humans, TLRs are believed to be an important component of innate immunity. Human and Drosophila Toll protein sequences show homology over the entire length of the protein chains. The family of human Toll-like receptors is comprised of ten highly conserved receptor proteins, TLR1-TLR10. Like Drosophila toll, human TLRs are type I transmembrane proteins with an extracellular domain consisting of a leucine-rich repeat (LRR) domain that recognizes pathogen-associated molecular patterns (PAMPs), and a cytoplasmic domain that is homologous to the cytoplasmic domain of the human interleukin-1 (IL-1) receptor. Similar to the signaling pathways for both Drosophila toll and the IL-1 receptor, human Toll-like receptors signal through the NF-κB pathway.
Although the different mammalian TLRs share many characteristics and signal transduction mechanisms, their biological functions are very different. This is due in part to the fact that four different adaptor molecules (MyD88, TIRAP, TRIF and TRAF) are associated in various combinations with the TLRs and mediate different signaling pathways. In addition, different ligands for one TLR may preferentially activate different signal transduction pathways. Furthermore, the TLRs are differentially expressed in various hematopoietic and non-hematopoietic cells. Accordingly, the response to a TLR ligand depends not only on the signal pathway activated by the TLR, but also on the nature of the cells in which the individual TLR is expressed.
Toll-like receptor 3 (TLR3) has received considerable attention as a therapeutic target as TLR3 signaling has been implicated in inflammatory and autoimmune conditions. Patent application WO98/50547 provides the nucleic acid and amino acid sequence of the hTLR3 protein. De Bouteiller et al. (2005) J. Biol. Chem. 280(46): 38133-38145) disclose use of an anti-TLR3 antibody to bind cell surface TLR3. Antibody C1130 is stated to be activatory toward TLR3 and has been described in WO 2007/051164. Polyclonal antibodies that inhibited TLR3 were described in Cavassani et al. (2008) J. Exp. Med. 205: 2609-2621. WO 03/106499 and Matsumoto et al. (2003) J. Immunol. 171:3154-3162 describes an antibody corresponding to antibody clone TLR3.7 (eBioScience Inc., San Diego) reported to bind and inhibit cell surface TLR3 but not cell compartment TLR3 or in myeloid-lineage DC. WO 06/060513 describes an antibody C1068 which is reported to inhibit cytokine production in epithelial cells, which are reported to express TLR3 on the cell surface. PCT patent application WO2010/051470 provides further anti-TLR3 antibodies. Other anti-TLR3 antibodies for research use include polyclonal anti-TLR3 antibodies from R&D Systems Corp., antibody 40C1285 from Abcam and antibodies 619F7, 713E4, 716G10, IMG-5631 and -IMG-5348, all from lmgenex Corp.
However, among currently available anti-TLR3 antibodies, they are not optimally suited for use as therapeutic agents, e.g. to modulate TLR3 in vivo. For example, many suffer from lack of efficacy or affinity to their epitopes. There is therefore a need to provide improved antibodies directed to TLR3.